Many athletic populations report poor sleep, especially during intensive training and competition periods. Recently, diet has been shown to significantly affect sleep in general populations; however, little is known about the effect diet has on the sleep of athletically trained populations. With sleep critical for optimal recovery and sports performance, this systematic review aimed to evaluate the evidence demonstrating that dietary factors influence the sleep of athletically trained populations. Four electronic databases were searched from inception to May 2022, with primary research articles included if they contained a dietary factor(s), an outcome measure of sleep or sleepiness, and participants could be identified as ‘athletically trained’. Thirty-five studies were included, with 21 studies assessed as positive quality, 13 as neutral, and one as negative. Sleep or sleepiness was measured objectively in 46% of studies (n = 16). The review showed that evening (≥5 p.m.) caffeine intakes >2 mg·kg⁻¹ body mass decreased sleep duration and sleep efficiency, and increased sleep latency and wake after sleep onset. Evening consumption of high glycaemic index carbohydrates and protein high in tryptophan may reduce sleep latency. Although promising, more research is required before the impact of probiotics, cherry juice, and beetroot juice on the sleep of athletes can be resolved. Athletic populations experiencing sleep difficulties should be screened for caffeine use and trial dietary strategies (e.g., evening consumption of high GI carbohydrates) to improve sleep.

Summary: Insufficient sleep is a growing global problem, with poor sleep associated with many negative health and performance outcomes. Previous reviews investigating the effect of diet on sleep have highlighted the amino acid tryptophan as a promising sleep‐promoting nutrient, with the richest food source of tryptophan, ⍺‐lactalbumin, requiring further investigation. Therefore, this systematic review aimed to review the existing evidence of association between ⍺‐lactalbumin and sleep. Four electronic databases (CINAHL Complete, Embase, MEDLINE Complete, and SPORTDiscus with Full Text) were searched from database inception to March 2023, with primary research articles included if they contained α‐lactalbumin as an independent variable, an outcome measure of sleep or sleepiness, and participants were ≥ 18 years old. Eight studies were reviewed, with four studies recruiting athletic populations (50%) and four recruiting healthy participants (50%). Sleep or sleepiness was measured objectively in six studies (75%), with two studies employing polysomnography and four utilizing actigraphy to assess sleep. Across the studies, 20–60 g of ⍺‐lactalbumin was supplemented, with five studies (63%) observing a positive association between α‐lactalbumin and sleep. Sleep‐onset latency was the primary sleep metric improved following evening supplementation of α‐lactalbumin (≤ 3.5 hr pre‐sleep), with no studies observing any negative associations with sleep. Data from this review suggest that individuals that have difficulty initiating sleep may benefit most from pre‐sleep α‐lactalbumin supplementation. Further research is required to establish the effect that α‐lactalbumin has on sleep architecture, through the use of more comprehensive sleep analysis tools such as portable electroencephalography or polysomnography, in combination with stringent dietary controls.

Evening consumption of a whey protein rich in the amino acid tryptophan, alpha-lactalbumin (ALAC), has previously shown to benefit sleep—particularly among poor sleepers. Given trained populations often experience sleep difficulty, this study investigated whether evening supplementation of ALAC would influence sleep outcomes, mood, and next-day cognitive performance within a trained population with sleep difficulties. Nineteen trained participants (females, n = 11) with sleep difficulties (Athlete Sleep Screening Questionnaire: 8.1 ± 3.1; Pittsburgh Sleep Quality Index: 10.5 ± 4.1) completed this double-blinded, counterbalanced, randomized, crossover trial. Forty grams of ALAC or control were supplemented 2 hr presleep for three consecutive nights in a controlled environment, with sleep measured using dry electroencephalography. Blood samples were taken on the first evening of each experimental trial, with mood, sleepiness, and recovery assessed across the evening and morning. A cognitive testing battery was also completed each morning. During the ALAC condition, the primary findings were that participants had raised plasma tryptophan levels (p < .01), increased nonrapid eye movement Stage 2 sleep duration (CON: 205.9 ± 33.3; ALAC: 216.5 ± 33.1 min), reduced rapid eye movement duration (CON: 110.8 ± 27.9; ALAC: 99.7 ± 23.1 min), and improved reaction time in cognitive tests involving sensory motor speed, spatial orientation, and vigilant attention (p < .05). Data suggest evening supplementation of 40 g ALAC alters sleep architecture and improves next-morning reaction time in trained populations with sleep difficulties. Therefore, trained individuals experiencing sleep difficulty may benefit from acute ALAC supplementation to assist next-day performance. Future research should investigate this effect within habitual environments, outside of a tightly controlled setting.

Background: Many athletes experience sleep difficulties, and prior research within this cohort suggests that acute supplementation of alpha-lactalbumin (ALAC), a whey protein rich in the amino acid tryptophan, may improve sleep and performance. Therefore, this study investigated whether sub-chronic ALAC supplementation in the evening would improve sleep and physical performance within a poor-sleeping athletic population. Methods: In total, 24 athletically trained participants with sleep difficulties (Athlete Sleep Screening Questionnaire: 8.6 ± 2.2; Pittsburgh Sleep Quality Index: 10.0 ± 3.0) completed this double-blinded, randomised controlled, crossover trial. The participants were supplemented with 40 g of ALAC or control 2 h pre-sleep for seven consecutive nights within habitual settings, with sleep measured via actigraphy. Performance was assessed following the 1-week supplementation period, with the 30 s countermovement jump test, Yo-Yo Intermittent Recovery Test Level 1, and reaction time testing performed in a standardised sequence under controlled conditions. Results: During the ALAC condition, the objective number of awakenings increased (CON: 10.25 ± 5.28, ALAC: 11.01 ± 5.79; p = 0.031), the average jump height reduced (CON: 28.58 ± 5.53 cm, ALAC: 27.68 ± 5.14 cm; p = 0.037), the subjective physical and mental performance capabilities declined in the evening (p < 0.001), and evening negative emotional states (p = 0.001) were reduced. Conclusions: Seven days of ALAC supplementation may not improve the sleep and physical performance of an athletically trained population with mild–moderate sleep difficulties. Future research should recruit populations with more severe sleep difficulties and measure sleep architecture over an extended period to fully ascertain the effects, and potential benefits, of ALAC supplementation for athletes.

The Australian Football League Women's (AFLW) competition is comprised of a short, intensive competitive season, highlighting the importance of proper fuelling and recovery to support performance. Little is known about the dietary and sleep habits of AFLW athletes across a season, and the influence that age has on these behaviours. Therefore, this study aimed to determine the effects of season phase and age on dietary intake and sleep in elite AFLW athletes. Dietary intake and sleep were assessed in 22 AFLW athletes (25.9 ± 5.0 y) over 10 nights, including five consecutive nights during both pre‐season and in‐season. Dietary intake was quantified through self‐reported food diaries using a smartphone application (Easy Diet Diary), and sleep via a wearable monitoring device (Oura ring). Restricted maximum likelihood mixed models were used to determine variations in dietary intake and sleep in AFLW players between season phases (i.e., pre‐season vs. in‐season) and age. In‐season protein (115.15 ± 35.14 vs. 126.48 ± 40.10 g, p = 0.026) and fat intakes (72.93 ± 29.55 vs. 83.43 ± 33.14 g, p = 0.012) were significantly lower compared to pre‐season, with no differences in sleep measures observed between season phases. While age did not influence dietary intake, each additional year of age was associated with 8 min less sleep ( p = 0.001) and 4 min earlier wake times ( p = 0.032). These findings suggest that protein and fat intakes fluctuate across the seasons, with increasing age being a non‐modifiable risk factor for shorter sleep durations within AFLW athletes.